Carburetor fuel system



Aug. 17, 1965 D. N. ARNDT CARBURETOR FUEL SYSTEM 2 Sheets-Sheet 1 Filed NOV. 20, 1961 INVENTOR.

po/vaza /v. ARA/07- W 195 m N. Amman"? 39mm? mmmmm'rcm FUEL Filed Nov. 20, 1961 2 Sheets-Sheet 2 INVENTOR.

,afjwwvwdmm xv. lama 07" 1 9 TTOW/VEYS United States Patent 3,2tl1,ll97 CARhURETOR FUEL SYSTEM Donald N. Arndt, Cass City, Mich, assignor to Walbro Corporation, (lass @ity, Mich, a corporation of Michigan Filed Nov. 29, 1961, Ser. No. 153,577

2 Claims. ((31. 261-41) This invention relates to a carburetor fuel system and more particularly to a carburetor for small engines of the type having a fuel supply chamber, a horizontal venturi tube, and the usual choke valve and throttle valve in the tube.

It is an object of the present invention to provide an improved idle system. The idle system in conventional carburetors is composed of relatively small fuel and air passages in combination with small jets. This results in a rich emulsion of fuel and air that is discharged through small calibrated openings into the air stream flowing past the throttle valve.

Proper atomization of this rich emulsion is largely dependent upon the pressure drop across the throttle valve. On many Z-cycle engines, this pressure drop is insufiicient to break up or atomize the fuel. Frequently in a Z-cycle multicylinder engine, one or more cylinders will run rich while others will run lean, making it almost impossible to obtain good engine operation at idle and low engine speeds. Some attempts have been made to conquer this difliculty by drilling small holes in the throttie valve positioned such that the air will pick up the emulsion to divide the mixture evenly between the various cylinders. This has. been a trial anderror method which has brought inconsistent and unsatisfactory results.

it is an object of the present invention to solve this problem by incorporating relatively large air passages in the idle system with the result that very little air flows past the throttle valve in the idle position. The air is rather diverted through a large idle air passage which is discharged on the downstream side of the throttle valve.

The pressure drop across the throttle valve is suflicient to impose a rather high velocity to the air passing through the large idle air passage and the desired atomization of the fuel is obtained.

It is an object also to achieve an idle mixture which is not rich as compared with the conventional system and to keep the fuel in suspension rather than to permit it to fall out and collect and puddle on the walls of the induction system. In addition, the device contemplates an adjustable discharge tube for the air and fuel emulsion on the downstream side of the throttle making it possible to direct the emulsion and obtain excellent distribution between cylinders.

While this system is particularly useful in solving the problems of idling and low suspension in a 2-cycle engine, it is equally effective in improving the operation of a 4-cycle engine.

Other objects and features of the invention relating to details of construction and operation will be apparent in the following description and claims.

rawings accompany the disclosure and the various views thereof may be briefly described as:

FIGURE 1, a perspective view of the device showing the basic carburetor structure and the improvement passages.

FIGURE 2, a perspective view of a modified form of the invention utilizing an adjustable air inlet control.

FIGURE 3, a sectional view illustrating the relationship of the throttle valve to the idle passages.

FIGURE 4, a sectional view showing an optional idle passage directly to an engine manifold.

3,281,097 Patented Aug. 17, 1965 "ice Referring to the drawings:

A carburetor body has a fuel supply chamber 22 which can be controlled by a conventional fuel supply system such as a float. The carburetor body has a main venturi passage 24 nad would normally have a choke valve (not shown) mounted on a shaft in hole 26. The carburetor has a fuel entrance 28 in a depending porion 30 of the body, and this fuel passes upwardly into a nozzle 32 where it mixes with primary air at the area 34. A suitable air inlet 36 is provided for the nozzle to the area 34.

Fuel supply for the idling system is by-passed from the main fuel chamber 33 to a vertical passage 44 angling upward at 42 to a cross passage 44 controlled by an idle needle 46. Cross passage 44 joins with a horizontal pas-- sage along the top of the carburetor housing. The passage 59 in the housing is plugged at 52 at the inlet end of the venturi, and this passage receives air through a small vertical passage 54 opening to the entrance side of the carburetor passage, the passage 5% extending through the housing to a dead end wall 56.

As shown in FIGURE 2, the passage 5% has two ports in its lower wall, one port 58 being ahead of the throttle valve and one port being behind the throttle valve.

The port 653 has a tube 62 depending therefrom with a side opening 64. This tube is movable. on its own axis in the opening 66. The throttle valve consisting of the pivoted disc (lid is mounted on a horizontal axis in a conventional way on the far side of the venturi. The carburetor opens to the engine in an opening 7% at the far end of the carburetor housing which has a holding flange 72. Ports 5% and Gil are formed by drilling down through the top of the housing and the openings above the ports are then closed by plugs 74. A slightly modified structure is shown in FIGURES 2 and 3 where an axially movable member in the form of a control needle is provided to cooperate with a seat M in the passage 5! to control air entering through the port 54.

In FIGURE 4, a further modification is shown wherein the passage ST; is continued in a passage 82 which extends to the outer face of the carburetor at 34, connecting directly with the passage 86 in an engine manifold 83. r

The idle air passages $4 and 5d, 58 and s2. have an effective area approximately four times that of the normal area of idle fuel passages. This permits a fairly high quantity of air to by-pass the throttle valve when it is in the closed position. The amount of fuel can still be restricted by the control needle 46 but the quantity of air and fuel can move through the carburetor fairly fast in the idle phase. Thus, it will carry into the cylinders as an atomized emulsion rather than dribbling through in puddles and droplets. Also, it is possible to move the tube 62 so that the wall port 64. is directed in a way that the mixture will be evenly divided between the cylinders, thus permitting smooth operation of the engine at slow speeds.

As is stated above, the idle air passages of the present invention have a working area at least four times that of the normal area of idle passages. For example, in a working carburetor where the standard idle passage would probably have been /8 or smaller, an air passage for the idle system constructed according to the present invention is about in diameter, making the effective area a little over four times that of the previous passage. This is a radical change from the practice of the past wherein it was thought that the idle pas sages required a very small effective area to permit proper control of the idle speeds. The adjustment screws 46 and 8d permit control of the ratio of the etfective areas of passages 42 and 519 but the inherent dimensions of the passages also permits the ratio suggested above. In addition, the present construction permits directional control of the idle fuel mixture in a two-cylinder engine to get proper distribution between the cylinders. On a three-cylinder engine with a high power rating, a single carburetor for each cylinder can be used and this eliminates the problem of distribution.

In the past, it has been common practice to provide an idle stop screw to control the proper opening of the throttle valve for correct idle speed. The build-up of the carbon deposit and other foreign matter on the edge of the throttle valve has caused a fluctuation of the air flow and thus has required continuous adjustment. Permitting the idle air to flow through the large idle air passage 50 and to bypass around the throttle valve eliminates these difficulties and makes it possible to maintain a constant idle speed.

I claim:

1. In a liquid fuel feed system for an internal combustion engine having an intake manifold, the combination of a carburetor having a body with a throttle-controlled mixture passage having an inlet at one end and an outlet at the other end, the outlet of which, downstream from the throttle, is adapted to be connected to the manifold, a reservoir in said body for holding a body of fuel adjacent said mixture passage, a main fuel supply passage leading from said reservoir to a main fuel jet in the mixture passage, an idle fuel passage leading from said reservoir to a point adjacent said mixture passage, means in said idle fuel passage to adjust the flow of fuel therethrough, an idle mixture air passage spaced from but extending along said mixture passage and intersecting said idle fuel passage, said air passage having an effective area throughout its length approximately four times the effective area of the idle fuel passage, means in said air passage to adjust the flow of air therethrough, said air passage originating adjacent the inlet of said mixture passage and terminating adjacent the outlet of said mixture passage wherein said last means and said means in said idle fuel passage may be adjusted such that the relative effective cross-sectional area available for fluid flow in the air passage and the idle fuel passage can have a relationship of approximately four to one, and adjust- .i ment means at the outlet of the idle mixture air passage to direct a combination of fuel and air reaching said outlet in a predetermined direction, said direction being controllable relative to an intake manifold of an engine by said adjustment means at said outlet.

2. In a gas fuel feed system for an internal combustion engine having an intake manifold, the combination of a carburetor having a body with a throttle-controlled mixture passage with an aligned inlet and outlet, the outlet of which, beyond the throttle, is adapted to be connected to the manifold, a reservoir in said body for holding a body of fuel adjacent said mixture passage, a main fuel supply passage leading upward from said reservoir to a main fuel jet in the throat of said mixture passage, an idle fuel passage leading upward from said reservoir and around said mixture passage to the top of said body above said mixture passage, means in said idle fuel passage to adjust the flow of fuel therethrough, and an idle mixture air passage formed in said body along the top thereof above said mixture passage intersecting said idle fuel passage and having an effective area throughout its entire length substantially larger than the effective area of said idle fuel passage with an inlet adjacent the inlet of said mixture passage and an outlet adjacent the outlet of said mixture passage, the idle mixture air passage having its outlet at the outlet of the mixture passage adjacent tie manifold, and adjustable means at the outlet of the idle mixture air passage to direct the idle mixture therefrom in a predetermined adjusted posi tion relative to the manifold.

References Cited by the Examiner UNITED STATES PATENTS HARRY B. THORNTON, Primary Examiner.

HERBERT L. MARTIN, Examiner. 

1. IN A LIQUID FUEL FEED SYSTEM FOR AN INTERNAL COMBUSTION ENGINE HAVING AN INTAKE MANIFOLD, THE COMBINATION OF A CARBURETOR HAVING A BODY WITH A THROTTLE-CONTROLLED MIXTURE PASSAGE HAVINNG AN INLET AT ONE END ANND AN OUTLET AT THE OTHER END, THE OUTLET OF WHICH, DOWNSTREAM FROM THE THROTTLE, IS ADAPTED TO BE CONNECTED TO THE MANIFOLD, A RESERVOIR IN SAID BODY FOR HOLDING A BODY OF FUEL ADJACENT SAID MIXTURE PASSAGE, A MAIN FUEL SUPPLY PASSAGE LEADING FROM SAID RESERVOIR TO A MAIN FUEL JET IN THE MIXTURE PASSAGE, AN IDLE FUEL PASSAGE LEADING FROM SAID RESERVOIR TO A POINT ADJACENT SAID MIXTURE PASSAGE; MEAN IN SAID IDLE FUEL PASSAGE TO ADJUST THE FLOW OF FUEL THERETHROUGH, AN IDLE MIXUTE AIR PASSAGE SPACED FROM BUT EXTENDING ALONG SAID MIXTURE PASSAGE AND INTERSECTING SAID IDLEE FUEL PASSAGE, SAID AIR PASSAGE HAVING AN EFFECTIVE AREA THROUHOUT ITS LENGTH APPROXIMATELY FOUR TIMES THE EFFECTIVE AREA OF THE IDLE FUEL PASSAGE, MEANS IN SAID AIR PASSAGE TO ADJUST THE FLOW OF AIR THERETHROUGH, SAID AIR PASSAGE ORIGINATING ADJACENT THE INLET OF SAID MIXTURE PASSAGE AND TERMINATING ADJACENT THE OUTLET OF SAIDD MIXTURE PASSAGE WHEREIN SAID LAST MEANNS AND SAID MEANS IN SAID IDLE FUEL PASSAGE MAY BE ADJUSTED SUCH THAT THE RELATIVE EFFECTIVE CROSS-SECTIONAL AREA AVAILABLE FOR FLUID FLOW IN THE AIR PASSAGE AND THE IDLE FUEL PASSAGE CAN HAVE A RELATIONSHIP OF APPROXIMATELY FOUR TO ONE, AND ADJUSTMENT MEANS AT THE OUTLET OF THE IDLE MIXTURE AIR PASSAGE TO DIRECT A COMBINATION OF FUEL AND AIR REACHING SAID OUTLEET IN A PREDETERMINED DIRECTION, SAID DIRECTION BEING CONTROLLABLE RELATIVE TO AN INTAKE MANIFOLD OF AN ENGINE BY SAID ADJUSTMENT MEANS AT SAID OUTLET. 